We at WordPress.com consider all bloggers to own all of their own content.

In our Terms of Service, we say the following:

Our service is designed to give you as much control and ownership over what goes on your site as possible and encourage you to express yourself freely.

We do also say the following:

By submitting Content to Automattic for inclusion on your Website, you grant Automattic a world-wide, royalty-free, and non-exclusive license to reproduce, modify, adapt and publish the Content solely for the purpose of displaying, distributing and promoting your blog. If you delete Content, Automattic will use reasonable efforts to remove it from the Website, but you acknowledge that caching or references to the Content may not be made immediately unavailable.

Please note the part in bold. We do not claim ownership over the content - this section is necessary to allow us to display your content on our site generally (in other words, to have a website on our servers at all!) as well as in the Reader, related posts, etc. Elsewhere in the TOS we do also state that it is your responsibility to ensure that you own the rights to (or have permission to display) all of the content on your own site.

You are also always welcome to export your own content and use it elsewhere.